linux-kernel - Re: [PACTH v2 0/3] Implement /proc/<pid>/totmaps

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Message-ID: <20160830082049.GB23963@dhcp22.suse.cz>
Date:   Tue, 30 Aug 2016 10:20:50 +0200
From:   Michal Hocko <mhocko@...nel.org>
To:     Marcin Jabrzyk <m.jabrzyk@...sung.com>
Cc:     Sonny Rao <sonnyrao@...omium.org>, Jann Horn <jann@...jh.net>,
        Robert Foss <robert.foss@...labora.com>,
        Jonathan Corbet <corbet@....net>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Vlastimil Babka <vbabka@...e.cz>,
        Konstantin Khlebnikov <koct9i@...il.com>,
        Hugh Dickins <hughd@...gle.com>,
        Naoya Horiguchi <n-horiguchi@...jp.nec.com>,
        Minchan Kim <minchan@...nel.org>,
        John Stultz <john.stultz@...aro.org>,
        ross.zwisler@...ux.intel.com, jmarchan@...hat.com,
        Johannes Weiner <hannes@...xchg.org>,
        Kees Cook <keescook@...omium.org>,
        Al Viro <viro@...iv.linux.org.uk>,
        Cyrill Gorcunov <gorcunov@...nvz.org>,
        Robin Humble <plaguedbypenguins@...il.com>,
        David Rientjes <rientjes@...gle.com>,
        eric.engestrom@...tec.com, Janis Danisevskis <jdanis@...gle.com>,
        calvinowens@...com, Alexey Dobriyan <adobriyan@...il.com>,
        "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        ldufour@...ux.vnet.ibm.com, linux-doc@...r.kernel.org,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Ben Zhang <benzh@...omium.org>,
        Filipe Brandenburger <filbranden@...omium.org>,
        Mateusz Guzik <mguzik@...hat.com>
Subject: Re: [PACTH v2 0/3] Implement /proc/<pid>/totmaps

On Wed 24-08-16 12:14:06, Marcin Jabrzyk wrote:
[...]
> Sorry to hijack the thread, but I've found it recently
> and I guess it's the best place to present our point.
> We are working at our custom OS based on Linux and we also suffered much
> by /proc/<pid>/smaps file. As in Chrome we tried to improve our internal
> application memory management polices (Low Memory Killer) using data
> provided by smaps but we failed due to very long time needed for reading
> and parsing properly the file.

I was already questioning Pss and also Private_* for any memory killer
purpose earlier in the thread because cumulative numbers for all
mappings can be really meaningless. Especially when you do not know
about which resource is shared and by whom. Maybe you can describe how
you are using those cumulative numbers for your decisions and prove me
wrong but I simply haven't heard any sound arguments so far. Everything
was just "we know what we are doing in our environment so we know those
resouces and therefore those numbers make sense to us". But with all due
respect this is not a reason to add a user visible API into the kernel.

-- 
Michal Hocko
SUSE Labs